CS Malononitrile and CN

CS, or tear gas, is used frequently by the military and law enforcement as a method of controlling both individuals and crowds. The military also uses it during exercises to train personnel in the use of protective equipment. CN, known by its common name, Mace®, is the oldest of the crowd-control agents. CS was developed in the 1950s, and it has largely replaced the use of CN.

CS and CN are both lacrimating agents. CS is usually mixed with a pyrotechnic compound for dispersal in grenades or canisters as a fine particulate, which forms the characteristic smoke. CN is usually prepared for aerosol dispersal by individual canisters. Both agents are available in individual containers or large bombs, or they can be dispersed through a hand-held aerosolizer. They are formulated with several solvents, such as alcohol, ether, carbon sulfide, and methylchloroform (32), or can be dispersed as solid particles. In the United States, a combination of CS (10%) and PS (10%) is used by some law enforcement for chemical restraint.

CS and CN are highly soluble in numerous agents. When contact with mucous membranes is made, the symptoms described in Table 2 occur. Even though there is the perception of shortness of breath, pulmonary function tests performed shortly after exposure to either agent have shown minimal alterations (33). Its mechanism of irritation is not fully understood. The effects of CS are believed to be related to the formation of highly irritating chlorine atoms and hydrochloric acid when it comes in contact with water in mucous membranes (1,34). CS and CN have also been described as alkylating agents that target sulfhydryl groups (33). In addition, there is some controversy surrounding the production of cyanide molecules at the tissue level with exposure to high CS concentrations (35,36). Regardless, the effects of CS and CN are usually manifested without permanent tissue injury. Exposure is most often limited because exposed individuals will voluntarily flee the scene to avoid further exposure. Exposure can be significant if the affected person is forced into a confined space for extended periods of time.

A cluster of adverse events associated with CS exposure during a training exercise in the US Marines has been reported. Nine Marines were exposed to CS without the benefit of personal protective equipment. All participated in rigorous physical exercise within 3-4 d after exposure to CS and were subsequently hospitalized with various pulmonary symptoms, including cough, shortness of breath, hemoptysis (n = 5) and hypoxia (n = 4). Four required hospitalization in an intensive care setting, five in a non-monitored setting. All symptoms of respiratory distress abated within 72 hours of onset, and all nine Marines had normal lung function 1 week after CS exposure (37).

Most of the dispersal methods for CS and CN achieve concentrations far below what is considered to be lethal (38). However, there is some question regarding concentrations achieved near grenades or other delivery devices or for those who cannot or will not leave the exposure area (6,38). Based on animal studies, it is generally believed that a concentration of 25,000-150,000 mg/m3/min or 200 mg/kg body mass represents the LD50 for CS. A grenade can generate a concentration of 2000-5000 mg/m3 at the center, with concentrations becoming significantly less within a few yards from the center of the explosion (38). Regardless of the amount of exposure, all exposures that occur without the use of personal protective equipment where respiratory symptoms do not improve should be evaluated.

Treatment of CS exposure is based largely on the severity of clinical findings. The majority of patients will fully recover within minutes of removal from the agent and will not require medical attention (39). The most common lasting complaints are facial and ocular irritation. In contrast to other forms of chemical exposure, irrigating the affected area will only intensify and prolong the effects of CS gas or particles. For patients who require medical evaluation, the first order of treatment should always be removal of contaminated clothing with special attention to eliminating secondary exposure by using protective equipment and not placing a contaminated patient in a confined space. Clothing should be removed outside and placed inside a plastic bag, then bagged again. Blowing dry air directly onto the eye assists in vaporizing the dissolved CS gas (40). Some clinicians have recommended copious ocular irrigation with sterile saline, although this has been believed to cause an initial acute increase in ocular irritation (40,41) in some cases. A careful slit lamp examination of the anterior segment of the eye, including under the lids, should be done for persistent ocular irritation. If particles have become imbedded in the cornea or under the lids, they should be removed. If corneal abrasions are present, a few days of topical broad-spectrum antibiotics, cycloplegics, and appropriate analgesics in addition to close follow-up should be prescribed.

Dermal irritation in the form of burning and blistering can be treated with irrigation, preferably with an alkaline solution other than sodium hypo-chlorite (30). Erythema can be common in skin that has been freshly abraded but resolves 45-60 minutes after exposure. Contact dermatitis can be effectively treated with topical corticosteroids and/or antihistamines, such as diphen-hydramine. Typically, dermatitis associated with CS exposure resolves within a few days (30).

Home remedies, such as application of cooking oils, are contraindicated and pose an increase risk for irritation and infection (41). Sodium hypochlo-rite solutions will exacerbate any dermal irritation and should not be used. Plain soap and water is effective, but in most cases, removal of clothing in a well-ventilated area is all that is needed.

There are conflicting reports about the long-term effects of CS exposure. With an exposure to high concentrations, usually for prolonged periods in a

Options for Treatment for Exposure to Chemical Crowd-Control Agents

Treatment

PS

CS

CN

Removal of contaminated clothing

s

S

S

Ocular irrigation

s

S

Dermal irrigation

S

S

S

Alkaline solution irrigation of skin

S

S

Soap and water decontamination

S

S

S

Topical steroids for dermatitis

S

S

S

Systemic antihistamines for dermatitis

S

S

S

Systemic steroids for dermatitis

S

S

S

Topical antibiotics for corneal abrasion

S

S

S

Cycloplegics

S

S

S

Analgesics for pain

S

S

S

PS, pepper spray; CS, chlorobenzylidene; CN, chloracetothenon.

PS, pepper spray; CS, chlorobenzylidene; CN, chloracetothenon.

confined space, pulmonary edema, pneumonitis, heart failure, hepatocellular damage, and death have been reported (12,42). There are no data to support any claims of teratogenicity, or toxicity to the pregnant woman (12,43). These agents do not exacerbate chronic diseases, such as seizure disorders, respiratory disease, or psychiatric illnesses. Contact allergies in those previously exposed have also been reported (44-46).

The possibility of secondary exposure to health care and law enforcement providers exists with the use of chemical crowd-control agents. Although published reports are few, effects can be minimized with common sense practices, such as decontamination before the patient is placed in a confined area (e.g., police car, ambulance, or a confined room in the emergency department). The use of protective personal equipment, such as gloves and careful washing of exposed areas, avoids cross-contamination.

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